1. Field of the Invention
The invention pertains to stationary syphon systems for rotating heat exchanger rolls or drums utilizing a pivoted pick-up conduit wherein improved stability, efficiency, maintenance and installation characteristics are achieved.
2. Description of the Related Art
Rotating rolls and drums are commonly utilized to dry or heat moving webs during the manufacture of paper, cardboard, fabrics, and the like. In paper making and cardboard making mills, a plurality of rotating rolls or drums are used to sequentially engage the web to be heated or dried, and in modern mills, the tendency is for the rolls to operate at increasing rates of rotation to improve production.
Most heat exchanger rolls and drums utilized for drying are heated by steam injected into the roll through a rotary joint located at the end of one of the roll journals. The steam engages the inner surface of the roll or drum heating the roll periphery which is cooled by the transfer of heat to the web passing over the roll. The steam condensate, in a rapidly rotating roll, will be held against the roll inner chamber surface by centrifugal force and produces a thermal insulative barrier reducing the transfer of heat within the roll to the roll wall. Accordingly, it is highly desirable to remove the liquid condensate as quickly as possible to reduce the "rimming" condensate film thickness and improve the heat transfer characteristics between the steam and roll.
A variety of syphon systems are used with rotating rolls and drums for removing condensate. Basically, syphons fall into two categories. Rotary syphon systems utilize a pick-up shoe and conduit which is held against the roll or drum inner wall and rotates with the roll. The rotating syphon will withdraw condensate rimming 360.degree. throughout the interior of the roll and is effective to maintain a minimum thickness of condensate in a rapidly rotating roll or drum. The second type of syphon system utilizes a stationary syphon wherein the syphon pick-up conduit does not rotate with the roller drum and has an entrance or pick-up shoe located near the lowermost portion of the roll inner chamber for removing condensate that collects by gravity at such lowermost location.
Rotating and stationary syphon systems each have their advantages and disadvantages. Rotating syphons can best be installed in large diameter rolls or drums having relatively large access openings located in the drum end plate or end head wherein access to the interior of the roller drum is possible to permit installation of the syphon. Rotating syphon systems can maintain a minimal thickness of condensate film within the rotating roll as there is no relative movement between the drum inner surface and syphon pick-up shoe. However, because there is no relative movement between the roll and pick-up shoe when the roll is not rotating, or rotating at slow speeds, introduction of steam into the roll causes the condensate to puddle at the lowermost regions of the roll and if the pick-up shoe is not located at the lowermost drum interior portion, the upper regions of the roll will heat to a much greater extent than the lower roll regions due to the lack of insulation produced by the condensate causing a slight warping or bending of the roll altering the tolerances and concentricity of the roll as it rotates during start up.
Stationary syphon systems are often used with smaller diameter roll and drum heat exchangers wherein access to the drum interior is restricted, and stationary syphons are usually used within the rolls or drums employed in the cardboard or corrugated board industry where the diameter of the drying rolls is less than the diameter of rolls and drums used in the paper making industry. In order to install a stationary syphon within a rotating roll or drum of a diameter of approximately two feet, or the like, the usual practice is to employ a syphon system which includes a horizontal pipe or conduit within the roll journal and a pick-up pipe or conduit usually attached to the inner end of the horizontal conduit by a pivot. When installing such a stationary two-part syphon, the pick-up conduit is pivoted to substantially axially align with the horizontal conduit for insertion of both conduits through the journal bore. Once the pick-up conduit is located within the roll interior chamber, it is permitted to pivot downwardly under gravity force so that the lower end of the pick-up conduit will be located adjacent the roll chamber inner surface, and the upper end of the pick-up conduit will be in communication with the horizontal conduit. This type of device is shown in U.S. Pat. No. 2,732,228.
Stationary syphons of the above type utilizing a pivoted pick-up conduit have several disadvantages. First, because the lowermost end of the pick-up conduit is only maintained in its operative position in close proximity to the roll inner surface by its own weight, it is difficult to accurately locate the lowermost end relative to the roll inner surface due to vibration and impact with the condensate. If the pick-up conduit lower end engages the roll inner surface, an objectionable scraping and wear occurs. If the lowermost end of the pick-up Conduit is excessively spaced from the roll interior surface, an objectionable radial thickness of condensate exists within the roll substantially reducing the thermal efficiency of the roll and will produce uneven heating during start up.
Further, as stationary syphon systems using pivoted pick-up conduits are normally supported at a location remote from the pick-up conduit, such as at the outer end of the journal, or within the rotary joint, this cantilever type support of the horizontal conduit and pick-up conduit permits radial instability due to lateral forces imposed upon the syphon by the moving condensate which will cause a movement and vibration of the syphon system alternately increasing and decreasing the spacing between the pick-up conduit lower end and the roll interior surface. Such vibrational movement of the syphon conduits causes stress and fractures requiring high maintenance costs. Rotating rolls and drums using stationary syphon systems are also subject to uneven roll heating problems during roll standstill or slow rotation if excessive spacing occurs between the lower end of the pick-up conduit and roll inner surface, and such excessive spacing and undesirable depth of condensate will permit the upper regions of the roll to excessively heat producing warping and bending of the roll which alters the tolerances of the rotating components, affects concentricity and will result in uneven heating and drying profiles in the material being heated, paper and corrugated material may be shredded, and uneven gluing of paper runs may occur.